1. Field of the Invention
The present invention relates to an air conditioner, and more particularly, to a method for controlling an air conditioner, which is capable of preventing frost from being formed on the outer surface of a refrigerant line connected to an indoor unit.
2. Discussion of the Related Art
Generally, air conditioners are used to cool or heat a confined space such as a room or to clean indoor air, in order to provide a comfortable indoor environment for users. Such an air conditioner includes a refrigeration system including a compressor, a condenser, an expansion valve, and an evaporator.
Air conditioners are mainly classified into a separation type and an integrated type. In an integrated type air conditioner, indoor and outdoor units thereof are integrated. Such an integrated type air conditioner is directly installed on an outer wall or window of a house. In a separation type air conditioner, an indoor unit, in which a cooling/heat-radiating device is installed, and an outdoor unit, in which heat-radiating/cooling and compressing devices are installed, are separated from each other, and are connected to each other via a refrigerant line.
Separation type air conditioners are also classified into a general type wherein one indoor unit is connected to one outdoor unit, and a multi-unit type wherein a plurality of indoor units are connected to one outdoor unit.
Also, in accordance with structures and operation methods of cooling systems thereof, multi-unit air conditioners are classified into a switching type wherein all indoor units operate in the same operating mode, that is, in cooling mode or heating mode alone, and a simultaneous type wherein a part of the indoor units operate in cooling mode, and the remaining indoor unit or indoor units operate in heating mode.
Recently, simultaneous type air conditioners have been mainly developed because they can provide both the cooling and heating effects to provide a more comfortable indoor environment without being influenced by ambient temperature or environment.
Meanwhile, in conventional air conditioners, a decrease in the suction pressure of a compressor occurs when a cooling operation is continuously performed for a prolonged period of time. Such a decrease in the suction pressure of the compressor results in a decrease in the surface temperature of the refrigerant line which connects the indoor and outdoor units. As a result, moisture (vapor) contained in ambient air is condensed on the outer surface of the refrigerant line, and is then accumulated in the form of frost on the outer surface of the refrigerant line in accordance with a further decrease in the surface temperature of the refrigerant line. Such a phenomenon is called “frosting”.
When such frosting occurs on the outer surface of the refrigerant line, the heat exchange of the refrigerant with ambient air is inefficiently carried out. As a result, the frosting of the outer surface of the refrigerant line may become severe.
In order to melt the frost accumulated on the outer surface of the refrigerant line in the above-mentioned conventional air conditioners, a method for stopping indoor units, which are in operation, has been used. In accordance with this method, when a refrigerant line is maintained at sub-zero temperatures for a predetermined time or more, an indoor unit associated with the refrigerant line is stopped. The stopped indoor unit is operated again when the surface temperature of the refrigerant line increases to a predetermined temperature or more after passage of a certain time.
However, this method has a problem in that the indoor unit does not operate during the process for melting the frost accumulated on the outer surface of the refrigerant line, so that it is impossible to supply comfortable air to the user in the room in which the indoor unit is installed.
Since the above-mentioned method is adapted to simply melt the frost already accumulated on the outer surface of the refrigerant line, there is also a problem in that the temperature of air discharged to the room may be too low to supply comfortable air to the user, even before the stopping of the indoor unit.
Furthermore, the frost accumulated on the outer surface of the refrigerant line degrades the heat exchanging capability of the air conditioner, so that the air conditioner exhibits a degraded heat exchanging efficiency.